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1. Field of the Invention (Technical Field)
The present invention relates to an apparatus and method for determining in the field the range to target, and for adjusting the sight/aiming point to compensate for bullet drop or drift at that range, for a firearm, specifically for a firearm equipped with a telescopic sight having a mildot type of reticle.
2. Background Art
The mildot reticle is in increasingly widespread use by long-range rifle shooters as a means of estimating the range to the target. This estimation is critical in order to correct for the varying degree of projectile drop (and/or wind drift) as different ranges and thereby enable the shooter to hit the target. With training and familiarization, and by using the mildot reticle and then making the appropriate calculations, an experienced marksman can accurately estimate the range to target.
Initially incorporated into telescopic gun sights designed for military (and later police) use, the mildot reticle is the object of growing acceptance in the civilian sector among target shooters and hunters. By using a set of fixed dots within the telescopic sight, the shooter can compare the size of a target, a portion of the target, or a nearby reference target when viewed through the sight to the series of precisely sized and spaced dots on the reticle. On a mildot reticle, the dots are uniformly center-to-center spaced at 1 mil, which spacing appears to subtend a length of approximately 36 inches on a target viewed at 1000 yards. By estimating the size of the target or a reference near the target, and noting the number of mils that equal the size of the target, the shooter can apply a formula to calculate the range to target. This formula is simply expressed as: size of target in yards multiplied by 1000, and that product then divided by size of target in mils, equals range in yards. Currently, this calculation is performed in the field using a conventional hand-held electronic calculator.
The present method of using a mildot reticle poses several serious challenges to the shooter. The necessary calculations are somewhat complex, and depend upon the shooter's ability to correctly remember and apply the formula. Dimensional analysis further complicates the process, as the size of the target more often than not is mentally estimated in inches, necessitating an additional calculation to convert the target size into a decimal equivalent of yards. The shooter generally must carry and use an electronic digital calculator, necessitating numerous data entry steps.
Even after the shooter has performed the range calculation procedure, the amount of the bullet drop (or wind drift) applicable to the known range must be applied to the sight picture to enable an accurate aim that will result in a hit on target. Either the telescopic sight must be mechanically adjusted, or the sighting point (the intersection of the cross hairs) "held over," to correct the elevation (and/or windage) of the gun barrel to compensate for the effects of gravity and/or wind. Determining this compensation necessitates a second series of calculations to convert the needed amount of elevation or windage correction into a gun sight adjustment or hold-over figure for the known range and load.
Besides presenting many opportunities for arithmetic error, the correction calculations are time consuming, which may prove problematic in certain scenarios, such as military or law enforcement counter-sniping operations, timed competitive target-shooting events, or hunting situations.
A need remains, therefore, for a calculator apparatus which eliminates the multiple data entry steps and simplifies the calculation procedures for determining range to target and/or elevation adjustment to compensate for bullet drop or drift over the range determined. The present invention was developed to satisfy this previously unmet need.